Leukocytes are one of components contained in the blood and act to remove foreign materials having intruded into the body from the outside. Either when infected with bacteria or viruses, a human body develops a fever. The number of leukocytes increases in the case of bacteria infection, whereas the number of lymphocytes increases but the number of leukocytes is held normal or decreases in the case of virus infection. Therefore, measuring leukocytes can distinguish between the bacterial infection and the virus infection.
Automatic blood cell counters utilizing electric resistivity methods have conventionally been used for measuring leukocytes (see, for example, Patent Literature 1). However, since the automatic blood cell counters are special instruments with a large size, leukocyte measurement devices which enable POC (Point of Care) tests at the time of examining outpatients in small- and medium-sized hospitals and at bedside have been desired.
An example of such leukocyte measurement devices is one using a carrier such as a porous membrane. For example, Patent Literature 2 discloses a leukocyte measurement device which measures the peroxidase activity due to myeloperoxidase in leukocytes (granulocytes in particular). This leukocyte measurement device lyses or disrupts leukocytes, so as to release myeloperoxidase, and then detects how a hydrogen peroxide decomposition reaction is promoted by the myeloperoxidase according to a change in the color of an oxidation-sensitive chromogenic donor dye on a porous membrane.
For example, Patent Literature 3 discloses a leukocyte measurement device using the esterase activity as an indicator. This leukocyte measurement device detects the hydrolysis activity due to esterase according to coloration of a chromogenic substrate such as 3-acetyl indoxyl on a porous membrane. When using this leukocyte measurement device, the blood of a subject as whole blood is dropped onto the device, so as to capture leukocytes, other blood components such as erythrocytes are removed with a wash solution as being caused to flow down therethrough, and then the esterase activity is measured.